1. Field of the Invention
The present invention relates to a sampling probe for a sample contained in a high pressure and high temperature fluid or reaction chamber, the sampling probe utilizing a multiple internal reflection (MIR) element having a cylindrical body with a reflective end and a curved end. The reflective end and an adjacent active portion of the probe body are positioned against or in the sample. The sampling probe is easily removed from and accurately reinstalled in the fluid or reaction chamber.
2. Description of Prior Art
This invention principally relates to a non-destructive reaction monitoring probe preferably using infrared spectroscopy. The invention utilizes an optics system operative to internally reflect source infrared radiation a number of times off an MIR element surface in contact with the fluid or sample under analysis and then to direct the remaining radiation (as modified by the infrared absorbtion characteristics of the fluid or sample) to a detector for analysis of the fluid or sample. Specifically, the invention is preferably directed to an optical system including a probe extending into the reaction chamber for IR spectroscopic analysis and monitoring of reactions being conducted under or fluids being subjected to elevated pressures and/or temperatures.
In the the infrared range, practically all organic (and many inorganic) molecules have characteristic spectra that positively identify them. In one such identification method, infrared energy is reflected along the length of the crystal by the physical phenomenon of total internal reflection. A fluid sample or reaction placed in contact with the crystal selectively absorbs different frequencies of IR energy from the crystal. The energy that is not absorbed exits the crystal and is directed to a detector which measures the distribution of energy absorbed by the fluid or reaction so as to obtain and display its infrared spectra. Sting U.S. Pat. No. 4,595,833 (assigned to the assignee of the present invention), Messerschmidt U.S. Pat. No. 4,730,882 (assigned to the assignee of the present invention) and Gilbey U.S. Pat. No. 3,669,545 illustrate different systems for employing an MIR crystal to analyze a fluid or solid in contact therewith.
Sting U.S. Pat. No. 4,595,833 discloses reflaxicon optics for directing infrared radiation from a source into the cone shaped entry end of a cylindrically shaped MIR crystal. The non-absorbed radiant energy leaves the cone shaped exit end of the MIR crystal and is transmitted through additional reflaxicon optics toward a detector. The cylindrically shaped MIR element is sealed into a tubular member in order to provide a sample chamber or cell for the fluid and fluidized samples being analyzed.
Messerschmidt U.S. Pat. No. 4,730,882 discloses an elongated flat MIR crystal having a first surface, a slightly longer second surface and beveled entry and exit end surfaces interconnecting the same. The radiant energy enters at right angles through the second surface, reflects off the beveled entry surface, reflects between the second and first surfaces in multiple reflections along the length of the crystal and reflects off the beveled exit end surface through the second surface to a detector.
The circular MIR crystal of U.S. Pat. No. 4,595,833 and the flat, beveled ended MIR crystal of U.S. Pat. No. 4,730,882 have been successfully commercially sold in sampling assemblies to analyze fluids and solids. These MIR crystal elements require special assembly, disassembly and maintenance procedures within the analysis chamber. These MIR crystals, as currently mounted, are not preferred for high pressure and/or temperature fluid monitoring because of the possibility of the MIR crystal breaking. In addition, the crystals, as currently mounted, are positioned in the chamber presenting obstructions to mixing or fluid flow.
Gilbey U.S. Pat. No. 3,669,545 discloses a crystal MIR probe used prior to the Gilbey patent application as well as the crystal MIR probes disclosed by Gilbey. The prior art MIR crystal probe is illustrated in FIG. 1 of Gilbey and includes a rectangular body having a 90.degree. "roof" at one end and a flat surface at its other end. The 90.degree. "roof" end provides (a) an angled, flat entry surface to admit infrared energy for multiple internal reflections along the MIR crystal and (b) an oppositely angled, flat exit surface for emitting the infrared energy that has been reflected back. Therefore, the prior art MIR crystal disclosed in Gilbey provides entry and exit of the infrared energy from the opposed flat sides of the "roof" at the same end of the rectangular crystal.
The MIR crystal designs proposed by Gilbey include a rectangular body having beveled or angled ends. The infrared energy enters one side of the body and is reflected off one beveled end of the body in alignment therewith for multiple internal reflections along that body. The radiant energy is reflected off the other crystal end and is then multiply reflected in the opposite direction for return to and exit from the same beveled face. All embodiments of the Gilbey patent disclose a class of crystals in which one face serves simultaneously to both totally reflect entering energy into the crystal and transmit exiting energy out of the crystal.
All of the rectangular MIR crystal bodies disclosed in the Gilbey patent are difficult to seal, particularly in high pressure and/or high temperature applications. The hole through the holder must be broached or a multiple piece holder used. In addition, the rectangular crystal bodies are not easily mounted in or removed from the reaction cell and reassembly requires both precise positioning and orientation of the crystal for accurate spectroscopic measurements.